Ferrite material

ABSTRACT

There can be provided an NiCuZn-based ferrite material containing an iron oxide, a copper oxide, zinc oxide and a nickel oxide in predetermined amounts as main components and a bismuth oxide, a silicon oxide, magnesium oxide and a cobalt oxide in predetermined amounts as additional components. Due to the predetermined amounts of the additional components, the ferrite material has an extremely good temperature characteristic (a change in permeability along with a change in temperature is small), a high quality coefficient Q and high strength.

TECHNICAL FIELD

A first group invention of the present invention relates to anNiCuZn-based ferrite material having an initial permeability μi of notlower than 200, particularly to a ferrite material having goodtemperature dependence of initial permeability, a high qualitycoefficient Q and high strength. The ferrite material of the presentinvention can be suitably used in, for example, a resin-mold-typeferrite component.

Further, a second group invention of the present invention relates to anNiCuZn-based ferrite material having an initial permeability μi of nothigher than 100, particularly to a ferrite material having goodtemperature dependence of initial permeability, a high qualitycoefficient Q and high strength. The ferrite material of the presentinvention can be suitably used in, for example, a resin-mold-typeferrite component.

Still further, a third group invention of the present invention relatesto an NiCuZn-based ferrite material as described above, particularly toa ferrite material used in a resin-mold-type ferrite component.

BACKGROUND ART

(1) In recent years, demands for components such as resin-mold-type chipinductor and stationary coil are rapidly growing in the fields of atelevision, a video recorder, a mobile communication device and thelike. The products in such fields are demanded to have suchcharacteristics as a small size, light weight and high accuracy, andalong with the demand, demands for a decrease in tolerance and anincrease in reliability to the above components are growing.

Meanwhile, a ferrite is commonly used in the core material of thesecomponents. In the case of a resin-mold-type inductor component, acompressive stress is produced in the core by resin molding, and theinductance value of the ferrite changes according to this compressivestress. Therefore, it is difficult to obtain a high-qualityresin-mold-type inductor component having small inductance tolerance.

Under the circumstances, a ferrite which undergoes a small change ininductance when an external force is applied, that is, a ferrite havinggood stress resistance is desired. Further, to increase the reliabilityof a device using an inductance component, it is important to increasethe reliability of the inductance component itself, specifically, todecrease the temperature dependence of initial permeability of theferrite used in the inductance component.

In response to such a demand, a variety of improvement techniques inthis field have heretofore been made. That is, in Japanese PatentApplication Laid-Open No. 326243-1993, an NiCuZn-based ferritecontaining 0.05 to 0.60 wt % of Co₃O₄, 0.5 to 2 wt % of Bi₂O₃ and 0.10to 2.00 wt % of a combination of SiO₂ and SnO₂ is proposed. However,since the NiCuZn-based ferrite contains a small amount of ZnO, a highinitial permeability of not lower than 200 cannot be obtained.

Further, in Japanese Patent No. 267916, an NiCuZn-based ferritecontaining 0.05 to 0.60 wt % of Co₃O₄, 3 to 5 wt % of Bi₂O₃ and 0.10 to2.00 wt % of SiO₂ is proposed. However, since the NiCuZn-based ferritecontains a small amount of ZnO, a high initial permeability of not lowerthan 200 cannot be obtained.

Further, in Japanese Patent Application Laid-Open No. 103953-1989, anNiZn based ferrite containing 0.05 to 2 wt % of Bi₂O₃, 0 to 1 wt % ofSiO₂ and MgO or an oxide of Mn is proposed. Although the NiZn basedferrite has improved heat shock resistance, its temperature dependenceof initial permeability cannot be said to be satisfactory.

Further, in Japanese Patent Application Laid-Open No. 228108-1989, anNiCuZn-based ferrite containing SiO₂ in an amount of 0.03 wt % or less,MnO in an amount of 0.1 wt % or less, Bi₂O₃ in an amount of 0.1 wt % orless and MgO in an amount of 0.1 wt % or less to form a structure foralleviating the stress is proposed. However, since the NiCuZn-basedferrite contains a small amount of Bi₂O₃, its stress resistance cannotbe said to be satisfactory.

Further, in Japanese Patent Application Laid-Open No. 325056-1996, anNiZn based ferrite material containing CoO, Bi₂O₃ and SiO₂ to make achange in inductance under a load extremely small and increase a Q valueat high frequency is disclosed.

However, as seen in the example disclosed in the gazette, the maincomposition of the example is out of the range of the main compositionof the present invention and does not include MgO of the presentinvention. Therefore, the value of a quality coefficient Q is liable tobe low.

In addition, in the case of a conventional NiCuZn ferrite containingBi₂O₃ and having high initial permeability, since its grain sizediameter is large, a temperature coefficient is low and the Q is high,so that a ferrite component having high strength cannot be obtained.

(2) As described above, in recent years, demands for components such asresin-mold-type chip inductor and stationary coil are rapidly growing inthe fields of a television, a video recorder, a mobile communicationdevice and the like. The products in such fields are demanded to havesuch characteristics as a small size, light weight and high accuracy,and along with the demand, demands for a decrease in tolerance and anincrease in reliability to the above components are growing.

Meanwhile, a ferrite is commonly used in the core material of thesecomponents. In the case of a resin-mold-type inductor component, acompressive stress is produced in the core by resin molding, and theinductance value of the ferrite changes according to this compressivestress. Therefore, it is difficult to obtain a high-qualityresin-mold-type inductor component having small inductance tolerance.

Under the circumstances, a ferrite which undergoes a small change ininductance when an external force is applied, that is, a ferrite havinggood stress resistance is desired. Further, to increase the reliabilityof a device using an inductance component, it is important to increasethe reliability of the inductance component itself, specifically, todecrease the temperature dependence of initial permeability of theferrite used in the inductance component.

In response to such a demand, a variety of improvement techniques inthis field have heretofore been made. That is, in Japanese PatentApplication Laid-Open No. 326243-1993, an NiCuZn-based ferritecontaining 0.05 to 0.60 wt % of Co₃O₄, 0.5 to 2 wt % of Bi₂O₃ and 0.10to 2.00 wt % of a combination of SiO₂ and SnO₂ is proposed. However,although the NiCuZn-based ferrite has improved stress resistance, Q islow and its temperature dependence of initial permeability is notsatisfactory, either.

Further, in Japanese Patent No. 267916, an NiCuZn-based ferritecontaining 0.05 to 0.60 wt % of Co₃O₄, 3 to 5 wt % of Bi₂O₃ and 0.10 to2.00 wt % of SiO₂ is proposed. However, as in the case of the aboveferrite, its temperature dependence of initial permeability cannot besaid to be satisfactory and its quality coefficient Q is also low.

Further, in Japanese Patent Application Laid-Open No. 103953-1989, anNiZn based ferrite containing 0.05 to 2 wt % of Bi₂O₃, 0 to 1 wt % ofSiO₂ and MgO or an oxide of Mn is proposed. Although the NiZn basedferrite has improved heat shock resistance, its temperature dependenceof initial permeability cannot be said to be satisfactory and itsquality coefficient Q is also low.

Further, in Japanese Patent Application Laid-Open No. 228108-1989, anNiCuZn based ferrite containing SiO₂ in an amount of 0.03 wt % or less,MnO in an amount of 0.1 wt % or less, Bi₂O₃ in an amount of 0.1 wt % orless and MgO in an amount of 0.1 wt % or less to form a structure foralleviating the stress is proposed. However, since the NiCuZn-basedferrite contains a small amount of Bi₂O₃, neither sufficient strengthnor sufficient temperature dependence of initial permeability isobtained.

Further, in Japanese Patent Application Laid-Open No. 325056-1996, anNiZn based ferrite material containing CoO, Bi₂O₃ and SiO₂ to make achange in inductance under a load extremely small and increase the Qvalue at high frequency is disclosed.

However, as seen in the example disclosed in the gazette, the maincomposition of the example is out of the range of the main compositionof the present invention and does not include MgO of the presentinvention. Therefore, the value of the quality coefficient Q is liableto be low.

(3) A nickel-based ferrite material (such as an NiCuZn-based ferrite,NiCu-based ferrite or Ni-based ferrite) is widely used as an inductorelement. Meanwhile, along with rapid developments in the fields ofinformation and telecommunication and high frequency in recent years,demand for an improvement in the performance of a resin-mold-typeinductor element or the like.

When the resin-mold-type inductor element is prepared, a ferritematerial is molded into a resin, and a compressive stress is exerted onthe ferrite material when the resin is cured. Since the inductance valueof the ferrite material changes according to the degree of thecompressive stress, a ferrite material which exhibits a small inductancechange caused by the compressive stress and has excellent stressresistance is desired for the resin-mold-type inductor element. As forthe improvements in the performance of the inductor element, a gentlechange in permeability along with a change in temperature and a large Qvalue which is a quality coefficient in a frequency band used aredesired.

To respond to such desires, an NiCuZn-based ferrite material containingcobalt oxide, bismuth oxide and silicon oxide is disclosed in JapanesePatent No. 2679716, Japanese Patent Application Laid-Open No.326243-1993 and the like. Further, an NiZn-based ferrite materialcontaining bismuth oxide and silicon oxide to have heat shock resistanceimproved is disclosed in Japanese Patent Application Laid-Open No.103953-1989, and an NiCuZn-based ferrite material containing siliconoxide, manganese oxide, bismuth oxide and magnesium oxide to have astress-alleviating structure is disclosed in Japanese Patent ApplicationLaid-Open No. 228108-1989. Further, a heat-shock-resistant ferritematerial having an average grain size diameter of crystal structure of20 to 60 μm is disclosed in Japanese Patent Application Laid-Open No.323806-1992, and an NiCuZn-based ferrite material containing 2.1 to 10.0wt % of silicon oxide is disclosed in Japanese Patent ApplicationLaid-Open No. 325056-1996.

However, the above NiCuZn-based ferrite material disclosed in JapanesePatent No. 2679716 and Japanese Patent Application Laid-Open No.326243-1993 contains zinc oxide in a small amount of 2 to 30 mol %, sothat high initial permeability μi cannot be obtained. Further, the NiZnbased ferrite material disclosed in Japanese Patent ApplicationLaid-Open No. 103953-1989 contains a small amount of cobalt oxide, sothat a change in permeability along with a change in temperature islarge, and the NiCuZn-based ferrite material disclosed in JapanesePatent Application Laid-Open No. 228108-1989 contains bismuth oxide inan amount of 0.1 wt % or less, so that its stress resistance is notsatisfactory. Further, the heat-shock-resistant ferrite materialdisclosed in Japanese Patent Application Laid-Open No. 323806-1992 has alarge average grain size diameter of crystal structure of 20 to 60 μm,so that a change in permeability along with a change in temperature islarge, and the NiCuZn-based ferrite material disclosed in JapanesePatent Application Laid-Open No. 325056-1996 contains a large amount ofsilicon oxide, so that a change in permeability along with a change intemperature is large.

Therefore, a ferrite material having high initial permeability,excellent stress resistance and a low absolute value of temperaturecoefficient is desired.

DISCLOSURE OF THE INVENTION

The present invention has been invented to solve the above problems ofthe prior art.

That is, the first group invention of the present invention has beeninvented for solving the problem in the above (1) of the prior art. Anobject thereof is to solve the problem of the above (1) and provide anNiCuZn-based ferrite material having a high initial permeability of notlower than 200, good temperature dependence of initial permeability, ahigh quality coefficient Q and high strength.

To achieve such an object, the present invention is an NiCuZn-basedferrite material containing, as main components, an iron oxide in anamount of 47.0 to 50.0 mol % in terms of Fe₂O₃, a manganese oxide in anamount of 0.3 to 1.5 mol % in terms of Mn₂O₃, a copper oxide in anamount of 2.0 to 8.0 mol % in terms of CuO, zinc oxide in an amount of30.1 to 33.0 mol % in terms of ZnO and a nickel oxide (NiO) in mol % asthe balance, wherein 0.5 to 6.0 wt % of bismuth oxide in terms of Bi₂O₃,0.1 to 2.0 wt % of silicon oxide in terms of SiO₂ and 0.05 to 1.0 wt %of magnesium oxide in terms of MgO are further contained in addition tothe main components.

Further, the present invention is an NiCuZn-based ferrite materialcontaining, as main components, an iron oxide in an amount of 47.0 to50.0 mol % in terms of Fe₂O₃, a manganese oxide in an amount of 0.3 to1.5 mol % in terms of Mn₂O₃, a copper oxide in an amount of 2.0 to 8.0mol % in terms of CuO, zinc oxide in an amount of 30.1 to 33.0 mol % interms of ZnO and a nickel oxide (NiO) in mol % as the balance, wherein0.5 to 6.0 wt % of bismuth oxide in terms of Bi₂O₃ and 0.15 to 3.2 wt %of talc are further contained in addition to the main components.

Further, the present invention has an initial permeability μi at afrequency of 100 kHz of not lower than 200.

The second group invention of the present invention has been inventedfor solving the problem in the above (2) of the prior art. An objectthereof is to solve the problem of the above (2) and provide anNiCuZn-based ferrite material which undergoes an extremely small changein inductance when an external force is applied and which has excellentstress resistance, good temperature dependence of initial permeabilityand a high quality coefficient Q.

To achieve such an object, the present invention is an NiCuZn-basedferrite material containing, as main components, an iron oxide in anamount of 47.0 to 50.0 mol % in terms of Fe₂O₃, a manganese oxide in anamount of 0.01 to 3.0 mol % in terms of Mn₂O₃, a copper oxide in anamount of 0.5 to 4.9 mol % in terms of CuO, zinc oxide in an amount of1.0 to 23.0 mol % in terms of ZnO and a nickel oxide in mol % in termsof NiO as the balance, wherein 0.02 to 1.0 wt % of cobalt oxide in termsof CoO, 0.5 to 10.0 wt % of bismuth oxide in terms of Bi₂O₃, 0.1 to 2.0wt % of silicon oxide in terms of SiO₂ and 0.05 to 1.0 wt % of magnesiumoxide in terms of MgO are further contained in addition to the maincomponents.

Further, the present invention is an NiCuZn-based ferrite materialcontaining, as main components, an iron oxide in an amount of 47.0 to50.0 mol % in terms of Fe₂O₃, a manganese oxide in an amount of 0.01 to3.0 mol % in terms of Mn₂O₃, a copper oxide in an amount of 0.5 to 4.9mol % in terms of CuO, zinc oxide in an amount of 1.0 to 23.0 mol % interms of ZnO and a nickel oxide in mol % in terms of NiO as the balance,wherein 0.02 to 1.0 wt % of cobalt oxide in terms of CoO, 0.5 to 10.0 wt% of bismuth oxide in terms of Bi₂O₃ and 0.15 to 3.2 wt % of talc arefurther contained in addition to the main components.

Further, the present invention has an initial permeability μi at afrequency of 100 kHz of not higher than 100.

The third group invention of the present invention has been invented forsolving the problem in the above (3) of the prior art. An object thereofis to provide an inexpensive ferrite material which has high initialpermeability and excellent stress resistance and which exhibits a smallinductance change caused by a compressive stress and a gentle change inpermeability along with a change in temperature.

To achieve such an object, the ferrite material of present invention isa ferrite material containing an iron oxide, a copper oxide, zinc oxideand a nickel oxide as main components, wherein the iron oxide iscontained in an amount of 46.0 to 49.0 mol % in terms of Fe₂O₃, thecopper oxide is contained in an amount of 4.0 to 11.0 mol % in terms ofCuO, the zinc oxide is contained in an amount of 30.1 to 33.0 mol % interms of ZnO and the nickel oxide is contained as the balance, and inaddition to these main components, 0.005 to 0.03 wt % of cobalt oxide interms of CoO, 0.1 to 0.5 wt % of bismuth oxide in terms of Bi₂O₃, 0.1 to0.6 wt % of silicon oxide in terms of SiO₂ and 0.05 to 1.0 wt % ofmagnesium oxide in terms of MgO are further contained as additionalcomponents.

Further, the ferrite material of the present invention is a ferritematerial containing an iron oxide, a copper oxide, zinc oxide and anickel oxide as main components, wherein the iron oxide is contained inan amount of 46.0 to 49.0 mol % in terms of Fe₂O₃, the copper oxide iscontained in an amount of 4.0 to 11.0 mol % in terms of CuO, the zincoxide is contained in an amount of 30.1 to 33.0 mol % in terms of ZnOand the nickel oxide is contained as the balance, and in addition tothese main components, 0.005 to 0.03 wt % of cobalt oxide in terms ofCoO, 0.1 to 0.5 wt % of bismuth oxide in terms of Bi₂O₃ and 0.1 to 2.0wt % of talc are further contained as additional components.

Further, the above ferrite material has an initial permeability at afrequency of 100 kHz of not lower than 200.

Further, the above ferrite material has a relative coefficient oftemperature dependence of initial permeability in a range of ±5 (ppm/°C.).

In addition, the above ferrite material has a rate of change ininductance under a pressure of 98 MPa in a range of ±5%.

BEST MODE OF EMBODYING THE INVENTION

A detailed description will be given to the embodiments of the presentinvention hereinafter.

(1) Description of the Invention of the First Invention Group

A detailed description will be given to the ferrite material of thepresent invention hereinafter. The ferrite material of the presentinvention contains, as its substantial main components, an iron oxide inan amount of 47.0 to 50.0 mol % (particularly preferably 47.5 to 49.5mol %) in terms of Fe₂O₃, a manganese oxide in an amount of 0.3 to 1.5mol % (particularly preferably 0.3 to 1.2 mol %) in terms of Mn₂O₃, acopper oxide in an amount of 2.0 to 8.0 mol % (particularly preferably3.0 to 7.0 mol %) in terms of CuO, zinc oxide in an amount of 30.1 to33.0 mol % (particularly preferably 30.1 to 32.0 mol %) in terms of ZnOand a nickel oxide in mol % in terms of NiO as the balance.

Further, the ferrite material of the present invention also contains abismuth oxide in an amount of 0.5 to 6.0 wt % (particularly preferably0.5 to 5.0 wt %) in terms of Bi₂O₃, a silicon oxide in an amount of 0.1to 2.0 wt % (particularly preferably 0.15 to 1.5 wt %) in terms of SiO₂and a magnesium oxide in an amount of 0.05 to 1.0 wt % (particularlypreferably 0.05 to 0.8 wt %) in terms of MgO, in addition to the abovemain components.

Talc contains Si and Mg in predetermined proportions as sinteringcomponents. Therefore, talc can be added in place of the above SiO₂ andMgO. In that case, to satisfy the above amounts of SiO₂ and MgO, talc isadded in an amount of 0.15 to 3.2 wt %.

In the above composition, when the content of Fe₂O₃ is lower than 47 mol%, the inconvenience that initial permeability lowers occurs, while whenthe content of Fe₂O₃ is higher than 50.0 mol %, the inconvenience that aquality coefficient Q becomes smaller occurs. When the content of Mn₂O₃is lower than 0.3 mol %, the inconvenience that the initial permeabilitylowers occurs, while when the content of Mn₂O₃ is higher than 1.5 mol %,the inconvenience that the quality coefficient Q becomes smaller occurs.When the content of CuO is lower than 2.0 mol %, the inconvenience thatthe initial permeability lowers occurs, while when the content of CuO ishigher than 8.0 mol %, the inconvenience that the quality coefficient Qbecomes smaller occurs.

When the content of ZnO is lower than 30.1 mol %, the inconvenience thatthe initial permeability lowers occurs, while when the content of ZnO ishigher than 33.0 mol %, the inconvenience that a Curie point becomeslower is liable to occur.

When the content of Bi₂O₃ is lower than 0.5 wt %, a sintered densitybecomes lower, so that the inconvenience that the strength of a sinteredbody lowers occurs. On the other hand, when the content of Bi₂O₃ ishigher than 6.0 wt %, the inconvenience that the quality coefficient Qbecomes smaller is liable to occur.

When the content of SiO₂ is lower than 0.1 wt %, the quality coefficientQ is liable to become smaller, while when the content of SiO₂ is higherthan 2.0 wt %, the initial permeability is liable to lower.

When the content of MgO is lower than 0.05 wt %, the quality coefficientQ is liable to become smaller, while when the content of MgO is higherthan 2.0 wt %, the initial permeability is liable to lower.

As for the case where the above SiO₂ and MgO are substituted by talc,when the content of talc is lower than 0.15 wt %, the qualitycoefficient Q is liable to become smaller, while when the content oftalc is higher than 3.2 wt %, the initial permeability is liable tolower.

In the present invention, to the above main components, CoO may also beadded in an amount of 0.02 to 0.6 wt %, particularly preferably 0.05 to0.5 wt %, as an additional component. Although CoO is added primarilyfor increasing the quality coefficient Q, the initial permeabilitylowers when the amount of CoO becomes too large and exceeds 0.6 wt %.

The NiCuZn-based ferrite material of the present invention relates to aferrite material having an initial permeability μi of not lower than200. Primarily, it is suitably used in such an application as a tuningcoil which requires a high Q value in a band ranging from 0.1 to 2.0MHz.

The ferrite material of the present invention, for example, is moldedinto a core material having a predetermined shape, wrapped around bynecessary windings and then resin-molded (resin-coated) to be used as afixed inductor, a chip inductor or the like. These are used, forexample, as a variety of electronic equipment in mobile communicationdevices such as a television, a video recorder, a portable telephone andan automobile telephone. The shape of the core is not particularlylimited. An example of the core is a drum-type core having an externaldiameter of not larger than 2 mm and a length of not larger than 2 mm.

A resin used as a molding material (coating material) may be athermoplastic or thermosetting resin, for example. Specific examples ofthe resin include a polyolefin, a polyester, a polyamide, apolycarbonate, a polyurethane, a phenol resin, an urea resin and anepoxy resin. Illustrative examples of means for molding the moldingmaterial include dipping, coating, spraying, injection molding and castmolding.

An example of the constitution of a chip inductor using the ferritematerial of the present invention will be presented below. For example,the chip inductor comprises a cylindrical core molded from the ferritematerial of the present invention and having a large-diameter rig onboth sides, a winding wound around the barrel of the core, electrodeterminals disposed on both sides of the core for connecting the edges ofthe wiring to an external electric circuit and fixing the core in aresin, and a resin molded to cover these components.

Next, a description will be given to an example of a method forproducing a ferrite by using the ferrite material of the presentinvention.

Firstly, a mixture is prepared by mixing predetermined amounts of rawmaterials as the main components with predetermined amounts of rawmaterials as the additional components such that the proportions ofthese components in the mixture fall within the ranges specified by thepresent invention.

Then, the mixture is calcined. The calcination is carried out in anoxidizing atmosphere, for example, in the air. The calcinationtemperature is preferably 800 to 1,000° C., and the calcination time ispreferably 1 to 3 hours. Then, the resulting calcined mixture is milledby a ball mill or the like to predetermined sizes. When the mixture ismilled, raw materials as the additional components may be added to andmixed into the mixture. Further, the raw materials as the additionalcomponents may be added such that some of the raw materials are addedbefore the calcination and the rest of them are added after thecalcination.

After the calcined mixture is milled, an appropriate amount of bindersuch as a polyvinyl alcohol is added and the resulting product is moldedinto a desired shape.

Then, the molded compact is sintered. The sintering is carried out in anoxidizing atmosphere, generally in the air. The sintering temperature isabout 950 to 1,100° C., and the sintering time is about 2 to 5 hours.

The present invention will be described in more detail with reference tospecific examples.

EXPERIMENT EXAMPLE I

As shown in the following Table 1, predetermined amounts of Fe₂O₃,Mn₂O₃, NiO, CuO and ZnO as main components and predetermined amounts ofCoO (added as required), Bi₂O₃ and either talc or a combination of SiO₂and MgO were mixed together in a ball mill for 16 hours. The additionalcomponents shown in Table 1 are expressed in wt % based on the maincomponents.

Further, these mixed powders were calcined in the air at 900° C. for 2hours and then mixed and milled in a ball mill for 16 hours. To theobtained ferrite powders, 10 wt % of 6% polyvinyl alcohol solution wasadded, and the resulting mixtures were granulated and molded under apressure of 98 MPa into rectangular molded compacts having a size of 50mm×5 mm×4 mm and toroidal molded compacts having an external diameter of20 mm, an inner diameter of 10 mm and a height of 5 mm. These moldedcompacts were sintered in the air at a sintering temperature of 1,080°C. for 2 hours to obtain rectangular core samples and toroidal coresamples which were made of ferrites.

Each of these samples was measured for (1) a relative coefficient oftemperature dependence (αμir), (2) initial permeability (μi) at 100 kHz,(3) a Q value at 500 kHz and (4) the strength of the sintered body.

The measurements of the above items (1) to (4) were carried out in thefollowing manner.

(1) Relative Coefficient of Temperature Dependence (αμir) and (2)Initial Permeability (pi) at 100 kHz

After a wire was wound around the toroidal core sample for 20 turns, aninductance value and the like were measured by an LCR meter, and arelative coefficient of temperature dependence (αμir) in the range from−20° C. to +60° C. and initial permeability (μi) at 100 kHz weredetermined.

The relative coefficient of temperature dependence (αμir) is a valueindicating a rate of change in initial permeability between twotemperatures. For example, when the initial permeability at thetemperature T₁ is μi₁ and the initial permeability at the temperature T₂is μi₂, αμir in the temperature range of T₁ to T₂ is expressed by thefollowing expression.

αμir=(μi ₂ −μi ₁)/μi ¹ ²(T ₂ −T ₁)

(3) O Value at 500 kHz

After a wire was wound around the toroidal core sample for 20 turns, a Qvalue was measured at a frequency of 500 kHz by an LCR meter.

(4) Strength

Three-point bending strength was measured using the rectangular coresample.

The results are shown in the following Table 1.

TABLE 1 Main Components (mol %) Additional Components (wt %) αμir QStrength Sample No. Fe₂O₃ Mn₂O₃ NiO CuO ZnO CoO Bi₂O₃ talc SiO₂ MgO μi(ppm) (500 kHz) (×10⁷ Pa) I-1(Comparison) 46.5 0.9 15.4 6.2 31.0 0 3.61.8 — — 175 7.3 92 17.5 I-2 47.0 0.9 14.9 6.2 31.0 0 3.6 1.8 — — 202 7.184 17.8 I-3 49.2 0.9 12.7 6.2 31.0 0 3.6 1.8 — — 236 6.3 56 18.2I-4(Comparison) 50.5 0.9 11.4 6.2 31.0 0 3.6 1.8 — — 348 2.2 23 19.5I-5(Comparison) 49.2 0.2 13.4 6.2 31.0 0 3.6 1.8 — — 186 6.8 62 18.5 I-649.2 0.3 13.3 6.2 31.0 0 3.6 1.8 — — 201 7.1 58 18.3 I-7 49.2 1.5 12.16.2 31.0 0 3.6 1.8 — — 284 8.5 51 19.3 I-8(Comparison) 49.2 2.0 11.6 6.231.0 0 3.6 1.8 — — 317 9.0 42 19.1 I-9(Comparison) 49.2 0.9 17.4 1.531.0 0 3.6 1.8 — — 186 −1.2 85 19.3 I-10 49.2 0.9 16.9 2.0 31.0 0 3.61.8 — — 201 −0.5 82 18.9 I-11 49.2 0.9 10.9 8.0 31.0 0 3.6 1.8 — — 2855.2 52 17.4 I-12(Comparison) 49.2 0.9 9.9 9.0 31.0 0 3.6 1.8 — — 304 8.739 17.4 I-13(Comparison) 49.2 0.9 13.7 6.2 30.0 0 3.6 1.8 — — 198 7.4 5818.2 I-14(Comparison) 49.2 0.9 10.2 6.2 33.5 0 3.6 1.8 — — 241 −9.8 4717.8 I-15 49.2 0.9 12.7 6.2 31.0 0.3 3.6 1.8 — — 205 8.9 58 18.4 I-1649.2 0.9 12.7 6.2 31.0 0.5 3.6 1.8 — — 201 9.8 61 18.2 I-17(Comparison)49.2 0.9 12.7 6.2 31.0 0.65 3.6 1.8 — — 196 11.5 63 18.7I-18(Comparison) 49.2 0.9 12.7 6.2 31.0 0 0.4 1.8 — — 164 10.1 32 12.4I-19(Comparison) 49.2 0.9 12.7 6.2 31.0 0 6.5 1.8 — — 261 −0.2 48 17.5I-20(Comparison) 49.2 0.9 12.7 6.2 31.0 0 3.6 0.1 — — 306 12.5 38 15.8I-21 49.2 0.9 12.7 6.2 31.0 0 3.6 0.15 — — 276 10.0 51 17.5I-22(Comparison) 49.2 0.9 12.7 6.2 31.0 0 3.6 3.5 — — 195 8.0 72 20.1I-23(Comparison) 49.2 0.9 12.7 6.2 31.0 0 3.6 — 0.05 0.60 351 7.9 4416.2 I-24 49.2 0.9 12.7 6.2 31.0 0 3.6 — 0.1 0.60 360 8.1 51 17.4 I-2549.2 0.9 12.7 6.2 31.0 0 3.6 — 2.0 0.60 203 9.9 50 18.9 I-26(Comparison)49.2 0.9 12.7 6.2 31.0 0 3.6 — 2.3 0.60 193 10.2 47 18.4I-27(Comparison) 49.2 0.9 12.7 6.2 31.0 0 3.6 — 1.2 0.03 300 8.0 45 18.6I-28 49.2 0.9 12.7 6.2 31.0 0 3.6 — 1.2 0.05 311 4.3 50 18.4 I-29 49.20.9 12.7 6.2 31.0 0 3.6 — 1.2 0.5 206 4.7 68 17.6 I-30(Comparison) 49.20.9 12.7 6.2 31.0 0 3.6 — 1.2 1.10 184 4.6 104 17.4 The sample No. I-14has a low Curie point of 118° C. and is treated as a comparative examplesample. Other samples have a Curie point of not lower than 120° C.

The effect of the present invention is obvious from the above result.That is, the present invention is an NiCuZn-based ferrite materialcontaining, as main components, an iron oxide in an amount of 47.0 to50.0 mol % in terms of Fe₂O₃, a manganese oxide in an amount of 0.3 to1.5 mol % in terms of Mn₂O₃, a copper oxide in an amount of 2.0 to 8.0mol % in terms of CuO, zinc oxide in an amount of 30.1 to 33.0 mol % interms of ZnO and a nickel oxide (NiO) in mol % as the balance, wherein0.5 to 6.0 wt % of bismuth oxide in terms of Bi₂O₃, 0.1 to 2.0 wt % ofsilicon oxide in terms of SiO₂ and 0.05 to 1.0 wt % of magnesium oxidein terms of MgO are further contained in addition to the maincomponents. Thus, an NiCuZn-based ferrite material having extremely goodtemperature dependence of initial permeability (rate of change inpermeability along with a change in temperature is small), a highquality coefficient Q and high strength can be obtained.

(2) Description of the Invention of the Second Invention Group

A detailed description will be given to the ferrite material of thepresent invention hereinafter. The ferrite material of the presentinvention is an NiCuZn-based ferrite material which contains, as itssubstantial main components, an iron oxide in an amount of 47.0 to 50.0mol % (particularly preferably 47.5 to 49.5 mol %) in terms of Fe₂O₃, amanganese oxide in an amount of 0.01 to 3.0 mol % (particularlypreferably 0.1 to 2.5 mol %) in terms of Mn₂O₃, a copper oxide in anamount of 0.5 to 4.9 mol % (particularly preferably 1.0 to 4.9 mol %) interms of CuO, zinc oxide in an amount of 1.0 to 23.0 mol % (particularlypreferably 1.0 to 22.0 mol %) in terms of ZnO and a nickel oxide in mol% in terms of NiO as the balance.

Further, the ferrite material of the present invention also contains acobalt oxide in an amount of 0.02 to 1.0 wt % (particularly preferably0.1 to 0.9 wt %) in terms of CoO, a bismuth oxide in an amount of 0.5 to10.0 wt % (particularly preferably 0.7 to 8.0 wt %) in terms of Bi₂O₃, asilicon oxide in an amount of 0.1 to 2.0 wt % (particularly preferably0.12 to 2.0 wt %) in terms of SiO₂ and a magnesium oxide in an amount of0.05 to 1.0 wt % (particularly preferably 0.05 to 0.9 wt %) in terms ofMgO, in addition to the above main components.

Talc contains Si and Mg in predetermined proportions as sinteringcomponents. Therefore, talc can be added in place of the above SiO₂ andMgO. In that case, to satisfy the above amounts of SiO₂ and MgO, talc isadded in an amount of 0.15 to 3.2 wt %.

In the above composition, when the content of Fe₂O₃ is lower than 47 mol%, the inconvenience that a change in permeability along with a changein temperature becomes larger occurs, while when the content of Fe₂O₃ ishigher than 50.0 mol %, the inconvenience that a quality coefficient Qbecomes smaller occurs. When the above predetermine amount of Mn₂O₃ iscontained, the value of the quality coefficient Q can be increased.However, when the amount of Mn₂O₃ becomes too large and exceeds theabove 3.0 mol %, the inconvenience that the value of the qualitycoefficient Q is decreased occurs.

When the content of CuO is higher than 4.9 mol %, the growth of abnormalgrains is liable to occur and the value of the quality coefficient Q isdecreased, while when the content of CuO is lower than 0.5 mol %, theinconvenience that a change in permeability along with a change intemperature becomes larger occurs.

When the content of ZnO is higher than 23.0 mol % or lower than 1.0 mol%, the inconvenience that the value of the quality coefficient Q isdecreased is liable to occur.

CoO is added primarily for increasing the quality coefficient Q andcontrolling the temperature dependence of initial permeability. However,when the amount of CoO becomes too large and exceeds 1.0 wt %, a changein permeability along with a change in temperature is liable to becomelarger suddenly. On the other hand, when the amount of CoO becomes toosmall and smaller than 0.02 wt %, the effect of decreasing a change inpermeability along with a change in temperature can be hardly seen.

When the content of Bi₂O₃ is lower than 0.5 wt %, a sintered densitybecomes lower, so that the inconvenience that the strength of a sinteredbody lowers occurs. On the other hand, when the content of Bi₂O₃ ishigher than 10.0 wt %, the inconvenience that a change in permeabilityalong with a change in temperature is liable to become larger.

When the content of SiO₂ is lower than 0.1 wt %, a change inpermeability along with a change in temperature is liable to becomelarger, while when the content of SiO₂ is higher than 2.0 wt %, thequality coefficient Q is liable to become smaller.

When the content of MgO is lower than 0.05 wt %, the quality coefficientQ is liable to become smaller and a change in permeability along with achange in temperature is liable to become larger, while when the contentof MgO is higher than 1.0 wt %, a change in permeability along with achange in temperature is liable to become larger.

As for talc correlated with the contents of the above SiO₂ and MgO, whenthe content of talc is lower than 0.15 wt %, a change in permeabilityalong with a change in temperature is liable to become larger. On theother hand, when the content of talc is higher than 3.2 wt %, thequality coefficient Q is liable to become smaller and a change inpermeability along with a change in temperature is liable to becomelarger.

The NiCuZn-based ferrite material of the present invention relates to aferrite material having an initial permeability μi of not higher than100. Primarily, it is suitably used in such an application as a tuningcoil which requires a high Q value in a band ranging from 0.5 to 250MHz.

The ferrite material of the present invention, for example, is moldedinto a core material having a predetermined shape, wrapped around bynecessary windings and then resin-molded (resin-coated) to be used as afixed inductor, a chip inductor or the like. These are used, forexample, as a variety of electronic equipment in mobile communicationdevices such as a television, a video recorder, a portable telephone andan automobile telephone. The shape of the core is not particularlylimited. An example of the core is a drum-type core having an externaldiameter of not larger than 2 mm and a length of not larger than 2 mm.

A resin used as a molding material (coating material) may be athermoplastic or thermosetting resin, for example. Specific examples ofthe resin include a polyolefin, a polyester, a polyamide, apolycarbonate, a polyurethane, a phenol resin, an urea resin and anepoxy resin. Illustrative examples of means for molding the moldingmaterial include dipping, coating, spraying, injection molding and castmolding.

An example of the constitution of a chip inductor using the ferritematerial of the present invention will be presented below. For example,the chip inductor comprises a cylindrical core molded from the ferritematerial of the present invention and having a large-diameter rig onboth sides, a winding wound around the barrel of the core, electrodeterminals disposed on both sides of the core for connecting the edges ofthe wiring to an external electric circuit and fixing the core in aresin, and a resin molded to cover these components.

Next, a description will be given to an example of a method forproducing a ferrite by using the ferrite material of the presentinvention.

Firstly, a mixture is prepared by mixing predetermined amounts of rawmaterials as the main components with predetermined amounts of rawmaterials as the additional components such that the proportions ofthese components in the mixture fall within the ranges specified by thepresent invention.

Then, the mixture is calcined. The calcination is carried out in anoxidizing atmosphere, for example, in the air. The calcinationtemperature is preferably 800 to 1,000° C., and the calcination time ispreferably 1 to 3 hours. Then, the resulting calcined mixture is milledby a ball mill or the like to predetermined sizes. When the mixture ismilled, raw materials as the additional components may be added to andmixed into the mixture. Further, the raw materials as the additionalcomponents may be added such that some of the raw materials are addedbefore the calcination and the rest of them are added after thecalcination.

After the calcined mixture is milled, an appropriate amount of bindersuch as a polyvinyl alcohol is added and the resulting product is moldedinto a desired shape.

Then, the molded compact is sintered. The sintering is carried out in anoxidizing atmosphere, generally in the air. The sintering temperature isabout 950 to 1,100° C., and the sintering time is about 2 to 5 hours.

The present invention will be described in more detail with reference tospecific examples.

EXPERIMENT EXAMPLE II

As shown in the following Table 2, predetermined amounts of Fe₂O₃,Mn₂O₃, NiO, CuO and ZnO as main components and predetermined amounts ofCoO, Bi₂O₃ and either talc or a combination of SiO₂ and MgO were mixedtogether in a ball mill for 16 hours. The additional components shown inTable 2 are expressed in wt % based on the main components.

Further, these mixed powders were calcined in the air at 900° C. for 2hours and then mixed and milled in a ball mill for 16 hours. To theobtained ferrite powders, 10 wt % of 6% polyvinyl alcohol solution wasadded, and the resulting mixtures were granulated and molded under apressure of 98 MPa into rectangular molded compacts having a size of 50mm×5 mm×4 mm and toroidal molded compacts having an external diameter of20 mm, an inner diameter of 10 mm and a height of 5 mm. These moldedcompacts were sintered in the air at a sintering temperature of 1,030°C. for 2 hours to obtain rectangular core samples and toroidal coresamples which were made of ferrites.

Each of these samples was measured for (1) a relative coefficient oftemperature dependence (αμir), (2) initial permeability (μi) at 100 kHz,(3) a Q value at 2 MHz and (4) the strength of the sintered body.

The measurements of the above items (1) to (4) were carried out in thefollowing manner.

(1) Relative Coefficient of Temperature Dependence (αμir) and (2)Initial Permeability (μi) at 100 kHz

After a wire was wound around the toroidal core sample for 20 turns, aninductance value and the like were measured by an LCR meter, and arelative coefficient of temperature dependence (αμir) in the range from−20° C. to +60° C. and initial permeability (μi) at 100 kHz weredetermined.

The relative coefficient of temperature dependence (αμir) is a valueindicating a rate of change in initial permeability between twotemperatures. For example, when the initial permeability at thetemperature T₁ is μi₁ and the initial permeability at the temperature T₂is μi₂, αμir in the temperature range of T₁ to T₂ is expressed by thefollowing expression.

αμir=(μi ₂ −μi ₁)/μi ₁ ²(T ₂ −T ₁)

(3) Q Value at 2 MHz

After a wire was wound around the toroidal core sample for 20 turns, a Qvalue was measured at a frequency of 2 MHz by an LCR meter.

(4) Strength

Three-point bending strength was measured using the rectangular coresample.

The results are shown in the following Table 2.

TABLE 2 Main Components (mol %) Additional Components (wt %) αμir QStrength Sample No. Fe₂O₃ Mn₂O₃ NiO CuO ZnO CoO Bi₂O₃ talc SiO₂ MgO μi(ppm) (2 kHz) (×10⁷ Pa) II-1(Comparison) 46.5 0.5 29.0 3.2 20.8 0.30 5.22.5 — — 32.7 26.2 209 16.8 II-2 47.0 0.5 29.0 3.2 20.3 0.30 5.2 2.5 — —33.5 19.7 198 17.4 II-3 49.3 0.5 29.0 3.2 18.0 0.30 5.2 2.5 — — 36.9 9.1179 15.6 II-4(Comparison) 50.5 0.5 29.0 3.2 16.8 0.30 5.2 2.5 — — 54.43.0 97 18.2 II-5(Comparison) 49.5 0 29.3 3.2 18.0 0.30 5.2 2.5 — — 36.29.3 99 15.6 II-6 47.5 2.0 29.3 3.2 18.0 0.30 5.2 2.5 — — 53.2 15.4 15518.6 II-7(Comparison) 47.5 3.2 28.8 3.2 17.3 0.30 5.2 2.5 — — 55.0 14.098 18.4 II-8(Comparison) 49.3 0.5 33.2 0.1 16.9 0.30 5.2 2.5 — — 26.621.0 268 14.5 II-9 49.3 0.5 32.7 0.5 17.0 0.30 5.2 2.5 — — 26.7 18.7 28215.1 II-10 49.3 0.5 29.0 4.8 16.4 0.30 5.2 2.5 — — 38.6 13.6 105 15.8II-11 49.3 0.52 9.0 5.0 16.2 0.30 5.2 2.5 — — 39.9 19.7 94 15.2(Comparison) II-12 49.3 0.54 7.0 3.0 0.2 0.30 5.2 2.5 — — 8.7 −14.3 8716.3 (Comparison) II-13 49.3 0.5 46.0 3.2 1.0 0.30 5.2 2.5 — — 10.1 −9.6104 16.0 II-14 49.3 0.52 3.5 3.2 23.5 0.30 5.2 2.5 — — 49.4 14.4 88 16.2(Comparison) II-15 49.3 0.52 9.0 3.2 18.0 0 5.2 2.5 — — 41.1 −0.7 10515.4 (Comparison) II-16 49.3 0.5 29.0 3.2 18.0 0.02 5.2 2.5 — — 40.5 0.5111 15.6 II-17 49.3 0.5 29.0 3.2 18.0 1.00 5.2 2.5 — — 34.2 18.6 21115.8 II-18 49.3 0.52 9.0 3.2 18.0 1.20 5.2 2.5 — — 33.1 25.9 227 16.2(Comparison) II-19 49.3 0.52 9.0 3.2 18.0 0.30 0.2 2.5 — — 22.4 19.9 1998.4 (Comparison) II-20 49.3 0.5 29.0 3.2 18.0 0.30 0.5 2.5 — — 22.1 19.7199 12.1 II-21 49.3 0.5 29.0 3.2 18.0 0.30 10.0 2.5 — — 34.2 19.9 18315.0 II-22 49.3 0.5 29.0 3.2 18.0 0.30 12.0 2.5 — — 31.3 24.6 175 15.9(Comparison) II-23 49.3 0.5 29.0 3.2 18.0 0.30 5.2 0 — — 79.9 23.5 19015.1 (Comparison) II-24 49.3 0.5 29.0 3.2 18.0 0.30 5.2 0.15 — — 75.419.8 174 15.4 II-25 49.3 0.5 29.0 3.2 18.0 0.30 5.2 2.6 — — 34.8 8.6 17816.2 II-26 49.3 0.5 29.0 3.2 18.0 0.30 5.2 3.5 — — 32.5 20.6 89 17.5(Comparison) II-27 49.3 0.5 29.0 3.2 18.0 0.30 5.2 — 0 0.80 47.8 22.2155 13.2 (Comparison) II-28 49.3 0.5 29.0 3.2 18.0 0.30 5.2 — 0.1 0.8048.3 19.3 156 14.5 II-29 49.3 0.5 29.0 3.2 18.0 0.30 5.2 — 1.7 0.80 39.710.3 129 15.6 II-30 49.3 0.52 9.0 3.2 18.0 0.30 5.2 — 2.1 0.80 38.1 10.185 17.0 (Comparison) II-31 49.3 0.5 29.0 3.2 18.0 0.30 5.2 — 1.7 0 58.332.1 81 15.8 (Comparison) II-32 49.3 0.5 29.0 3.2 18.0 0.30 5.2 — 1.70.05 50.8 18.2 105 14.9 II-33 49.3 0.5 29.0 3.2 18.0 0.30 5.2 — 1.7 0.9041.5 15.9 146 16.7 II-34 49.3 0.5 29.0 3.2 18.0 0.30 5.2 — 1.7 1.10 42.420.4 289 15.5 (Comparison) II-35 47.5 — 35.0 8.0 9.5 0.20 5.0 — 2.0 —34.0 33.4 71 19.3 (Comparison) II-36 49.3 0.02 29.0 3.2 18.48 0.2 3.02.5 — — 37.0 9.5 102 15.8

The effect of the present invention is obvious from the above result.That is, the present invention is an NiCuZn-based ferrite materialcontaining, as main components, an iron oxide in an amount of 47.0 to50.0 mol % in terms of Fe₂O₃, a manganese oxide in an amount of 0.01 to3.0 mol % in terms of Mn₂O₃, a copper oxide in an amount of 0.5 to 4.9mol % in terms of CuO, zinc oxide in an amount of 1.0 to 23.0 mol % interms of ZnO and a nickel oxide (NiO) in mol % as the balance, wherein0.02 to 1.0 wt % of cobalt oxide in terms of CoO, 0.5 to 10.0 wt % ofbismuth oxide in terms of Bi₂O₃, 0.1 to 2.0 wt % of silicon oxide interms of SiO₂ and 0.05 to 1.0 wt % of magnesium oxide in terms of MgOare further contained in addition to the main components. Alternatively,the present invention is an NiCuZn-based ferrite material containing, asmain components, an iron oxide in an amount of 47.0 to 50.0 mol % interms of Fe₂O₃, a manganese oxide in an amount of 0.01 to 3.0 mol % interms of Mn₂O₃, a copper oxide in an amount of 0.5 to 4.9 mol % in termsof CuO, zinc oxide in an amount of 1.0 to 23.0 mol % in terms of ZnO anda nickel oxide (NiO) in mol % as the balance, wherein 0.02 to 1.0 wt %of cobalt oxide in terms of CoO, 0.5 to 10.0 wt % of bismuth oxide interms of Bi₂O₃ and 0.15 to 3.2 wt % of talc are further contained inaddition to the main components. Thus, an NiCuZn-based ferrite materialhaving extremely good temperature dependence of initial permeability(rate of change in permeability along with a change in temperature issmall), a high quality coefficient Q and high strength can be obtained.

(3) Description of the Invention of the Third Invention Group

A description will be given to an embodiment of the present inventionhereinafter.

In the present invention, as a result of studying the contents of aniron oxide, a copper oxide, zinc oxide and a nickel oxide which are themain components of an NiCuZn-based ferrite material and the contents ofa cobalt oxide, a bismuth oxide and either a combination of a siliconoxide and magnesium oxide or talc which are the additional components ofthe NiCuZn-based ferrite material, a ferrite material having highinitial permeability μi, excellent stress resistance, a small inductancechange caused by a compressive stress and a gentle change inpermeability along with a change in temperature can be obtained when theabove contents are in predetermined ranges.

That is, the ferrite material of the present invention contains an ironoxide in an amount of 46.0 to 49.0 mol %, preferably 46.5 to 49.0 mol %,in terms of Fe₂O₃, a copper oxide in an amount of 4.0 to 11.0 mol %,preferably 5.0 to 9.0 mol %, in terms of CuO, zinc oxide in an amount of30.1 to 33.0 mol %, preferably 30.1 to 32.0 mol %, in terms of ZnO, anda nickel oxide (preferably in an amount of 7.0 to 20.0 mol % in terms ofNiO) as the balance. Further, the ferrite material of the presentinvention contains, as additional components, a cobalt oxide in anamount of 0.005 to 0.03 wt %, preferably 0.005 to 0.025 wt %, in termsof CoO, a bismuth oxide in an amount of 0.1 to 0.5 wt %, preferably 0.1to 0.45 wt %, in terms of Bi₂O₃, a silicon oxide in an amount of 0.1 to0.6 wt %, preferably 0.1 to 0.5 wt %, in terms of SiO₂, and magnesiumoxide in an amount of 0.05 to 1.0 wt %, preferably 0.05 to 0.8 wt %, interms of MgO, based on the above main components. Further, talc may beadded in place of the silicon oxide and magnesium oxide as additionalcomponents. Talc is added in an amount of 0.1 to 2.0 wt %, preferably0.15 to 1.8 wt %, based on the main components.

The ferrite material of the present invention has an initialpermeability μi of not lower than 200 at a frequency of 100 kHz.

Further, the ferrite material of the present invention has a smallrelative coefficient of temperature dependence αμir in absolute value ofinitial permeability. This relative coefficient of temperaturedependence αμir is a value indicating a rate of change in initialpermeability between two temperatures. For example, when the initialpermeability at the temperature T₁ is μi₁ and the initial permeabilityat the temperature T₂ is μi₂, αμir in the temperature range of T₁ to T₂is expressed by the following expression. The initial permeability μi₁is measured at a frequency of 100 kHz.

αμir=[(μi ₂ −μi ₁)/μi ₁ ²]×[1/(T ₂ −T ₁)]

The ferrite material of the present invention has a relative coefficientof temperature dependence αμir of initial permeability at 20 to 60° C.of ±5 (ppm/° C.). When the relative coefficient of temperaturedependence αμir is such a small value, the initial permeability is notsusceptible to temperature, so that when the ferrite material is used inan inductor element, its reliability is improved.

Further, the ferrite material of the present invention exhibits a smallinductance change caused by a compressive stress and has good stressresistance. For example, the ferrite material of the present inventionexhibits an inductance change rate ΔL/L×100 in a range of ±5% whenmonoaxially pressurized at a pressure of 98 MPa. L is an inductancebefore the material is pressurized, and ΔL is a rate of change ininductance caused by the pressurization. Since the ferrite material ofthe present invention has good stress resistance as described above, achange in inductance caused by molding of a resin can be reduced andhigh-precision electrical machinery and apparatus can be produced.

When the content of the iron oxide which is a main component of thepresent invention is lower than 46.0 mol %, the initial permeability μidecreases, while when the content is higher than 49.0 mol %, the valueof the quality coefficient Q decreases disadvantageously. Further, therequired content of the cobalt oxide increases to increase the Q value,which is not desirable from the viewpoint of production costs. Further,when the content of the copper oxide is lower than 4.0 mol %, a changein permeability along with a change in temperature becomes large, whilewhen the content of the copper oxide is higher than 11.0 mol %, the Qvalue decreases disadvantageously. Further, when the content of zincoxide is lower than 30.1 mol %, the stress resistance deteriorates,while when the content of zinc oxide is higher than 33.0 mol %, theCurie point becomes lower than 120° C., which is problematic inpractical use.

In addition, when the content of the cobalt oxide which is an additionalcomponent is lower than 0.005 wt % based on the main components, the Qvalue decreases, while when the content of the cobalt oxide is higherthan 0.03 wt %, the stress resistance deteriorates disadvantageously.When the content of the bismuth oxide which is an additional componentis lower than 0.1 wt % based on the main components, the stressresistance deteriorates, while when the content of the bismuth oxide ishigher than 0.5 wt %, a change in permeability along with a change intemperature becomes large disadvantageously. Further, when the contentof the silicon oxide which is an additional component is lower than 0.1wt % based on the main components, the stress resistance deteriorates,while when the content of the silicon oxide is higher than 0.6 wt %, theQ value decreases disadvantageously. Further, when the content ofmagnesium oxide which is an additional component is lower than 0.05 wt %based on the main components, the stress resistance deteriorates, whilewhen the content of magnesium oxide is higher than 1.0 wt %, a change inpermeability along with a change in temperature becomes largedisadvantageously. Further, when the content of talc which is used inplace of the silicon oxide and magnesium oxide as additional componentsis lower than 0.1 wt % based on the main components, the stressresistance deteriorates, while the content of talc is higher than 2.0 wt%, the initial permeability μi decreases disadvantageously.

The above ferrite material of the present invention can be produced bycalcining raw materials containing the iron oxide, copper oxide, zincoxide, nickel oxide, cobalt oxide, bismuth oxide, silicon oxide andmagnesium oxide or talc in such amounts that the proportions of thesecomponents in the composition of the ferrite material after calcinationwould be in the above ranges, molding the calcined powders into adesired form and sintering the molded compact (at 1,000 to 1,100° C.,for example).

Next, a detailed description will be given to the present invention withreference to specific examples.

EXAMPLE III

Preparation of Ferrite Material

Firstly, Fe₂O₃, CuO, ZnO and NiO as main components were weighed so thattheir weight ratios (mol %) should be those shown in the following Table3, and based on the composition of these main components, Bi₂O₃, CoO,SiO₂, MgO and talc were weighed so that their weight ratios (wt %)should be those shown in Table 3. Then, these materials were wet-blendedin a steel ball mill for 16 hours. Thereafter, the obtained mixedpowders were calcined at 900° C. for 2 hours and then mixed and milledin a ball mill for 16 hours.

Then, to the obtained milled powders, 10 wt % of 6% polyvinyl alcoholaqueous solution was added, and the resulting mixtures were granulated.The thus-obtained granules were press-molded under a pressure of 98 MPainto rectangular samples (width: 7 mm, thickness: 7 mm, length: 35 mm)and toroidal samples (external diameter: 20 mm, inner diameter: 10 mm,height: 5 mm). These molded compacts were sintered in the air at 1,000to 1,100° C. for 2 hours to obtain ferrite materials (samples 1 to 35).When the final compositions of the ferrite materials were measured byfluorescent X-ray spectroscopy, they corresponded to the initialcompositions.

Evaluations of Ferrite Materials

Each of the above ferrite materials (samples 1 to 35) was measured foran initial permeability μi, a relative coefficient of temperaturedependence αμir of initial permeability, stress resistance, a Q value asa quality coefficient and a Curie point Tc. The results are shown in thefollowing Table 3.

[Measurements of Initial Permeability and Relative Coefficient ofTemperature Dependence of Initial Permeability]

After a wire was wound around the obtained toroidal ferrite material for20 turns, an initial permeability μi at 100 kHz was measured by an LCRmeter (HP4192, product of Hewlett-Packard Company), and a relativecoefficient of temperature dependence αμir at temperatures ranging from20° C. to 60° C. was calculated from the following expression.

αμir=[(μi ₂ −μi ₁)/μi ₁ ²]×[1/(T ₂ −T ₁)]

(μi₁=initial permeability at temperature T₁)

(μi₂=initial permeability at temperature T₂)

[Measurement of Stress Resistance]

After a wire was wound around the barrel of the obtained rectangularsample for 20 turns, a monoaxial compressive force is applied to theresulting sample at a fixed speed. The inductance value of the sampleunder the application of the monoaxial compressive force was measuredcontinuously by an LCR meter (HP4285A, product of Hewlett-PackardCompany), and an inductance change rate was calculated from the obtainedmeasurements. The inductance change rate (ΔL/L×100) of each sample underthe application of a monoaxial compressive force of 1 t/cm² is shown inTable 3.

[Measurement of Quality Coefficient Q Value]

After a wire was wound around the obtained toroidal ferrite material for20 turns, a Q value at 100 kHz was measured by an LCR meter (HP4192A,product of Hewlett-Packard Company).

TABLE 3 Composition of Main Composition of Additional Stress Components(mol %) Components (wt %) αμir Resistance Samples Fe₂O₃ NiO CuO ZnO CoOBi₂O₃ talc SiO₂ MgO μi (ppm) (%) Q value Tc (° C.) Sample 1 46.5 15.58.0 31.0 0.010 0.20 0.35 0.00 0.00 141 −0.8 1.8 118 ≧120 Sample 2 46.015.0 8.0 31.0 0.010 0.20 0.35 0.00 0.00 203 −2.3 −0.9 134 ≧120 Sample 348.0 13.0 8.0 31.0 0.010 0.20 0.35 0.00 0.00 712 1.9 −3.8 135 ≧120Sample 4 49.0 12.0 8.0 31.0 0.010 0.20 0.35 0.00 0.00 532 4.7 −4.7 102≧120 Sample 5 49.1 11.9 8.0 31.0 0.010 0.20 0.35 0.00 0.00 524 5.6 −5.197 ≧120 Sample 6 48.0 17.3 3.7 31.0 0.010 0.20 0.35 0.00 0.00 586 5.6−4.1 153 ≧120 Sample 7 48.0 17.0 4.0 31.0 0.010 0.20 0.35 0.00 0.00 6134.9 −3.2 147 ≧120 Sample 8 48.0 10.0 11.0 31.0 0.010 0.20 0.35 0.00 0.00663 3.2 −3.8 101 ≧120 Sample 9 48.0 9.0 12.0 31.0 0.010 0.20 0.35 0.000.00 617 3.5 −4.1 88 ≧120 Sample 10 48.0 14.0 8.0 30.0 0.010 0.20 0.350.00 0.00 647 4.1 −5.1 164 ≧120 Sample 11 48.0 11.0 8.0 33.0 0.010 0.200.35 0.00 0.00 590 −2.0 −1.9 105 ≧120 Sample 12 48.0 10.0 8.0 34.0 0.0100.20 0.35 0.00 0.00 507 −13.5 −1.5 79 108 Sample 13 48.0 13.0 8.0 31.00.000 0.20 0.35 0.00 0.00 703 0.8 −2.3 95 ≧120 Sample 14 48.0 13.0 8.031.0 0.005 0.20 0.35 0.00 0.00 698 1.2 −2.5 106 ≧120 Sample 15 48.0 13.08.0 31.0 0.030 0.20 0.35 0.00 0.00 108 2.2 −4.9 152 ≧120 Sample 16 48.013.0 8.0 31.0 0.040 0.20 0.35 0.00 0.00 690 2.9 −5.3 165 ≧120 Sample 1748.0 13.0 8.0 31.0 0.010 0.05 0.35 0.00 0.00 754 3.2 −5.1 158 ≧120Sample 18 48.0 13.0 8.0 31.0 0.010 0.10 0.35 0.00 0.00 731 2.0 −4.3 143≧120 Sample 19 48.0 13.0 8.0 31.0 0.010 0.50 0.35 0.00 0.00 515 −4.2−2.2 149 ≧120 Sample 20 48.0 13.0 8.0 31.0 0.010 0.60 0.35 0.00 0.00 398−5.1 −2.0 164 ≧120 Sample 21 48.0 13.0 8.0 31.0 0.010 0.20 0.05 0.000.00 970 4.2 −5.2 112 ≧120 Sample 22 48.0 13.0 8.0 31.0 0.010 0.20 0.100.00 0.00 965 3.5 −4.9 121 ≧120 Sample 23 48.0 13.0 8.0 31.0 0.010 0.200.50 0.00 0.00 579 1.1 −2.5 144 ≧120 Sample 24 48.0 13.0 8.0 31.0 0.0100.20 2.00 0.00 0.00 193 4.9 −1.6 161 108 Sample 25 48.0 13.0 8.0 31.00.010 0.20 2.20 0.00 0.00 196 −0.1 −0.3 130 ≧120 Sample 26 48.0 13.0 8.031.0 0.010 0.20 0.00 0.05 0.11 892 2.5 −5.3 115 ≧120 Sample 27 48.0 13.08.0 31.0 0.010 0.20 0.00 0.10 0.11 873 2.1 −4.5 120 ≧120 Sample 28 48.013.0 8.0 31.0 0.010 0.20 0.00 0.30 0.11 598 1.3 −2.6 140 ≧120 Sample 2948.0 13.0 8.0 31.0 0.010 0.20 0.00 0.60 0.11 330 0.3 −1.1 108 ≧120Sample 30 48.0 13.0 8.0 31.0 0.010 0.20 0.00 0.70 0.11 307 0.8 −0.7 94≧120 Sample 31 48.0 13.0 8.0 31.0 0.010 0.20 0.00 0.27 0.00 672 1.8 −5.2128 ≧120 Sample 32 48.0 13.0 8.0 31.0 0.010 0.20 0.00 0.27 0.05 648 1.5−4.8 138 ≧120 Sample 33 48.0 13.0 8.0 31.0 0.010 0.20 0.00 0.27 0.20 6231.1 −2.6 152 ≧120 Sample 34 48.0 13.0 8.0 31.0 0.010 0.20 0.00 0.27 1.00373 −4.3 −2.5 159 ≧120 Sample 35 48.0 13.0 8.0 31.0 0.010 0.20 0.00 0.272.00 259 −5.1 −2.3 168 ≧120 *In the column of Curie Point Tc, “≧120”indicates that Tc is not lower than 120° C.

As shown in Table 3, the samples 2 to 4, 7, 8, 11, 14, 15, 18, 19, 22 to24, 27 to 29, 32 to 34 contain, as main components, Fe₂O₃ in an amountof 46.0 to 49.0 mol %, CuO in an amount of 4.0 to 11.0 mol %, ZnO in anamount of 30.1 to 33.0 mol % and NiO as the balance and also contain, asadditional components, CoO in an amount of 0.005 to 0.03 wt %, Bi₂O₃ inan amount of 0.1 to 1.0 wt %, SiO₂ in an amount of 0.1 to 0.6 wt % andMgO in an amount of 0.05 to 1.0 wt % or talc in an amount of 0.1 to 2.0wt % in place of SiO₂ and MgO based on the above main components. It hasbeen confirmed that they have an initial permeability μi at a frequencyof 100 kHz of not lower than 200, a relative coefficient of temperaturedependence αμir of initial permeability in a range of ±5 (ppm/° C.), arate of change in inductance under a pressure of 98 MPa in a range of±5% and a Curie point of not lower than 120° C.

Meanwhile, the samples other than those listed above have failed tosatisfy at least one the above four properties, that is, an initialpermeability μi at a frequency of 100 kHz of not lower than 200, arelative coefficient of temperature dependence αμir of initialpermeability in a range of ±5 (ppm/° C.), a rate of change in inductanceunder a pressure of 98 MPa in a range of ±5% and a Curie point of notlower than 120° C.

As described in detail above, according to the present invention, whenthe contents of the iron oxide, copper oxide, zinc oxide and nickeloxide as main components and the contents of the cobalt oxide, bismuthoxide and either a combination of silicon oxide and magnesium oxide ortalc as additional components are within predetermined ranges, a ferritematerial having high initial permeability, a gentle change inpermeability along with a change in temperature, a small inductancechange caused by a compressive stress and high stress resistance can beobtained. Further, since the content of cobalt oxide which is containedfor the purpose of attaining a gentle change in permeability along witha change in temperature is a very expensive material is significantlylow, an inexpensive ferrite material can be obtained.

INDUSTRIAL APPLICABILITY

The ferrite material of the present invention, for example, is moldedinto a core material having a predetermined shape, wrapped around bynecessary windings and then resin-molded (resin-coated) to be used as afixed inductor, a chip inductor or the like. These are used, forexample, as a variety of electronic equipment in mobile communicationdevices such as a television, a video recorder, a portable telephone andan automobile telephone.

What is claimed is:
 1. An NiCuZn-based ferrite material containing, asmain components, an iron oxide in an amount of 47.0 to 50.0 mol % interms of Fe₂O₃, a manganese oxide in an amount of 0.3 to 1.5 mol % interms of Mn₂O₃, a copper oxide in an amount of 2.0 to 8.0 mol % in termsof CuO, zinc oxide in an amount of 30.1 to 33.0 mol % in terms of ZnOand a nickel oxide in mol % in terms of NiO as the balance, wherein 0.5to 6.0 wt % of bismuth oxide in terms of Bi₂O₃, 0.1 to 2.0 wt % ofsilicon oxide in terms of SiO₂ and 0.05 to 1.0 wt % of magnesium oxidein terms of MgO are contained based on the main components.
 2. Theferrite material of claim 1, which further contains 0.02 to 0.6 wt % ofcobalt oxide in terms of CoO based on the main components.
 3. AnNiCuZn-based ferrite material containing, as main components, an ironoxide in an amount of 47.0 to 50.0 mol % in terms of Fe₂O₃, a manganeseoxide in an amount of 0.3 to 1.5 mol % in terms of Mn₂O₃, a copper oxidein an amount of 2.0 to 8.0 mol % in terms of CuO, zinc oxide in anamount of 30.1 to 33.0 mol % in terms of ZnO and a nickel oxide in mol %in terms of NiO as the balance, wherein 0.5 to 6.0 wt % of bismuth oxidein terms of Bi₂O₃ and 0.15 to 3.2 wt % of talc are contained based onthe main components.
 4. The ferrite material of claim 3, which furthercontains 0.02 to 0.6 wt % of cobalt oxide in terms of CoO based on themain components.
 5. The ferrite material of claim 1, which has aninitial permeability μi at a frequency of 100 kHz of not lower than 200.6. The ferrite material of claim 3, which has an initial permeability μiat a frequency of 100 kHz of not lower than
 200. 7. An electronic partcomprising an NiCuZn-based ferrite material, wherein the ferritematerial contains, as main components, an iron oxide in an amount of47.0 to 50.0 mol % in terms of Fe₂O₃, a manganese oxide in an amount of0.3 to 1.5 mol % in terms of Mn₂O₃, a copper oxide in an amount of 2.0to 8.0 mol % in terms of CuO, zinc oxide in an amount of 30.1 to 33.0mol % in terms of ZnO and a nickel oxide in mol % in terms of NiO as thebalance, and also contains 0.5 to 6.0 wt % of bismuth oxide in terms ofBi₂O₃, 0.1 to 2.0 wt % of silicon oxide in terms of SiO₂ and 0.05 to 1.0wt % of magnesium oxide in terms of MgO based on the main components. 8.An electronic part comprising an NiCuZn-based ferrite material, whereinthe ferrite material contains, as main components, an iron oxide in anamount of 47.0 to 50.0 mol % in terms of Fe₂O₃, a manganese oxide in anamount of 0.3 to 1.5 mol % in terms of Mn₂O₃, a copper oxide in anamount of 2.0 to 8.0 mol % in terms of CuO, zinc oxide in an amount of30.1 to 33.0 mol % in terms of ZnO and a nickel oxide in mol % in termsof NiO as the balance, and also contains 0.5 to 6.0 wt % of bismuthoxide in terms of Bi₂O₃ and 0.15 to 3.2 wt % of talc based on the maincomponents.
 9. An NiCuZn-based ferrite material containing, as maincomponents, an iron oxide in an amount of 47.0 to 50.0 mol % in terms ofFe₂O₃, a manganese oxide in an amount of 0.01 to 3.0 mol % in terms ofMn₂O₃, a copper oxide in an amount of 0.5 to 4.9 mol % in terms of CuO,zinc oxide in an amount of 1.0 to 23.0 mol % in terms of ZnO and anickel oxide in mol % in terms of NiO as the balance, wherein 0.02 to1.0 wt % of cobalt oxide in terms of CoO, 0.5 to 10.0 wt % of bismuthoxide in terms of Bi₂O₃, 0.1 to 2.0 wt % of silicon oxide in terms ofSiO₂ and 0.05 to 1.0 wt % of magnesium oxide in terms of MgO arecontained based on the main components.
 10. An NiCuZn-based ferritematerial containing, as main components, an iron oxide in an amount of47.0 to 50.0 mol % in terms of Fe₂O₃, a manganese oxide in an amount of0.01 to 3.0 mol % in terms of Mn₂O₃, a copper oxide in an amount of 0.5to 4.9 mol % in terms of CuO, zinc oxide in an amount of 1.0 to 23.0 mol% in terms of ZnO and a nickel oxide in mol % in terms of NiO as thebalance, wherein 0.02 to 1.0 wt % of cobalt oxide in terms of CoO, 0.5to 10.0 wt % of bismuth oxide in terms of Bi₂O₃ and 0.15 to 3.2 wt % oftalc are contained based on the main components.
 11. The ferritematerial of claim 9, which has an initial permeability μi at a frequencyof 100 kHz of not higher than
 100. 12. The ferrite material of claim 10,which has an initial permeability μi at a frequency of 100 kHz of nothigher than
 100. 13. An electronic part comprising an NiCuZn-basedferrite material, wherein the ferrite material contains, as maincomponents, an iron oxide in an amount of 47.0 to 50.0 mol % in terms ofFe₂O₃, a manganese oxide in an amount of 0.01 to 3.0 mol % in terms ofMn₂O₃, a copper oxide in an amount of 0.5 to 4.9 mol % in terms of CuO,zinc oxide in an amount of 1.0 to 23.0 mol % in terms of ZnO and anickel oxide in mol % in terms of NiO as the balance, and also contains0.02 to 1.0 wt % of cobalt oxide in terms of CoO, 0.5 to 10.0 wt % ofbismuth oxide in terms of Bi₂O₃, 0.1 to 2.0 wt % of silicon oxide interms of SiO₂ and 0.05 to 1.0 wt % of magnesium oxide in terms of MgObased on the main components.
 14. An electronic part comprising anNiCuZn-based ferrite material, wherein the ferrite material contains, asmain components, an iron oxide in an amount of 47.0 to 50.0 mol % interms of Fe₂O₃, a manganese oxide in an amount of 0.01 to 3.0 mol % interms of Mn₂O₃, a copper oxide in an amount of 0.5 to 4.9 mol % in termsof CuO, zinc oxide in an amount of 1.0 to 23.0 mol % in terms of ZnO anda nickel oxide in mol % in terms of NiO as the balance, and alsocontains 0.02 to 1.0 wt % of cobalt oxide in terms of CoO, 0.5 to 10.0wt % of bismuth oxide in terms of Bi₂O₃ and 0.15 to 3.2 wt % of talcbased on the main components.
 15. A ferrite material containing an ironoxide, a copper oxide, zinc oxide and a nickel oxide as main components,wherein the iron oxide is contained in an amount of 46.0 to 49.0 mol %in terms of Fe₂O₃, the copper oxide is contained in an amount of 4.0 to11.0 mol % in terms of CuO, zinc oxide is contained in an amount of 30.1to 33.0 mol % in terms of ZnO and the nickel oxide is contained as thebalance, and based on the main components, 0.005 to 0.03 wt % of cobaltoxide in terms of CoO, 0.1 to 0.5 wt % of bismuth oxide in terms ofBi₂O₃, 0.1 to 0.6 wt % of silicon oxide in terms of SiO₂ and 0.05 to 1.0wt % of magnesium oxide in terms of MgO are contained as additionalcomponents.
 16. A ferrite material containing an iron oxide, a copperoxide, zinc oxide and a nickel oxide as main components, wherein theiron oxide is contained in an amount of 46.0 to 49.0 mol % in terms ofFe₂O₃, the copper oxide is contained in an amount of 4.0 to 11.0 mol %in terms of CuO, zinc oxide is contained in an amount of 30.1 to 33.0mol % in terms of ZnO and the nickel oxide is contained as the balance,and based on the main components, 0.005 to 0.03 wt % of cobalt oxide interms of CoO, 0.1 to 0.5 wt % of bismuth oxide in terms of Bi₂O₃ and 0.1to 2.0 wt % of talc are contained as additional components.
 17. Theferrite material of claim 15, which has an initial permeability at afrequency of 100 kHz of not lower than
 200. 18. The ferrite material ofclaim 16, which has an initial permeability at a frequency of 100 kHz ofnot lower than
 200. 19. The material of claim 15, which has a relativecoefficient of temperature dependence of initial permeability in a rangeof ±5 (ppm/° C.).
 20. The material of claim 16, which has a relativecoefficient of temperature dependence of initial permeability in a rangeof ±5 (ppm/° C.).
 21. The material of claim 15, which has a rate ofchange in inductance under a pressure of 98 MPa in a range of ±5%. 22.The material of claim 16, which has a rate of change in inductance undera pressure of 98 MPa in a range of ±5%.
 23. An electronic partcomprising an NiCuZn-based ferrite material, wherein the ferritematerial contains, as main components, an iron oxide in an amount of46.0 to 49.0 mol % in terms of Fe₂O₃, a copper oxide in an amount of 4.0to 11.0 mol % in terms of CuO, zinc oxide in an amount of 30.1 to 33.0mol % in terms of ZnO and a nickel oxide as the balance, and alsocontains, as additional components, 0.005 to 0.03 wt % of cobalt oxidein terms of CoO, 0.1 to 0.5 wt % of bismuth oxide in terms of Bi₂O₃, 0.1to 0.6 wt % of silicon oxide in terms of SiO₂ and 0.05 to 1.0 wt % ofmagnesium oxide in terms of MgO based on the main components.
 24. Anelectronic part comprising an NiCuZn-based ferrite material, wherein theferrite material contains, as main components, an iron oxide in anamount of 46.0 to 49.0 mol % in terms of Fe₂O₃, a copper oxide in anamount of 4.0 to 11.0 mol % in terms of CuO, zinc oxide in an amount of30.1 to 33.0 mol % in terms of ZnO and a nickel oxide as the balance,and also contains, as additional components, 0.005 to 0.03 wt % ofcobalt oxide in terms of CoO, 0.1 to 0.5 wt % of bismuth oxide in termsof Bi₂O₃ and 0.1 to 2.0 wt % of talc based on the main components.